What does Catherine Ross mean when she says that "freedom of expression is the engine oil that makes democracies function"?

Catherine Ross believes that freedom of expression is critical to the functioning of a democracy.

However, she states that the educational system of the country is failing to promote freedom of speech among students. She believes that teachers are not doing enough in order to respect students right to express themselves and even engage in acts that aim to restrain youngster's expressions.

As a result, students graduate from school with a notion that authorities are distant and would be reluctant to listen to people's views. This produces citizens that are uninterested in participating in politics.